THURSDAY, Feb. 9 (HealthDay News) -- The longer Hispanic women live in the United States, the more likely they are to have a preterm birth, a new study says.

Researchers analyzed data from 2,141 Hispanic women with a prior live birth who took part in the U.S. National Health and Nutrition Examination Survey 1999-2006.

The study found that the frequency of preterm birth was 3.4 percent for women who had lived in the United States for less than 10 years, 7.4 percent for those who'd lived in the United States for more than 10 years, and 10 percent for those who were born in the United States.

The risk of preterm birth among the women in the study did not appear to be related to a number of preterm birth risk factors that were investigated in the study, the researchers noted.

They said their findings support the theory that preterm birth is, at least in part, related to environmental factors that are potentially preventable. However, it's still not clear which specific environmental factors increase or decrease the chances of preterm birth, the researchers said.

The study was slated to be presented Thursday at a meeting of the Society for Maternal-Fetal Medicine's annual meeting in Dallas.

Because this study was presented at a medical meeting, the data and conclusions should be viewed as preliminary until published in a peer-reviewed journal.